Process of producing alkali-metal cyanides



tatented anmA 22, i240 V B. JACOBS, '0F WILMINGTON, EWE, vASSIGNOR T0 E.I. DU PONT DE NEMQU et wl WE.

ANY, 0F WILMNGTN, D 5 l rnocass or rnonncme an WE, A CORPORATION @FDELA-f .t i' I-METL CYNXDES.

Application `filed February 28,1%9, Serial No. 279,801. Renewed June 15,i923.

To aZZ 'whom it may concern.'

Be it known that I, CHARLES B. JACOBS, a citizen of the United States,residing at Wilmington, in the county of New Castle and State ofDelaware, have invented new and usefullmprovements inv Processes .ofProducing Alkali-Metal Cyanides, of which the folowing is aspecification. This invention relates to a process of producingalkali-metal cyanides and pertains especially to a process in which freeor elemental nitrogen in a pure state, or free or elemental nitrogen 1nnitrogen bearing gases, is caused to combine directly, in the presenceof alkali-metal halides, with other compounds of the alkali-metas andwlth carbon to form alkali-metal cyanides.

The chief object of my invention is the formation of alkali-metalcyanides ai; lower temperatures, more economically, and in greateryields than have heretofore been obtainable by the reaction of gaseousnitrogen on compounds of the alkali-metals and carbon.

I am aware that it is not new to form alkali-metal cyanides by heatingalkalimetal carbonates and carbon to a high temperature in nitrogen.This was observed as early as the year 1829 by Desfosses.

I am also aware that the addition of certain metals or 'their reduciblecompounds such as finely divided iron, manganese, chromium, nickel,etc., to alkali-metal compounds and carbon, cause the formation ofalkali-metal cyanides to take place more abundantly and at lowertemperature, when these mixtures are heated in nitrogen, than is thecase when the alkali-metal compounds and carbon are heated alone innitrogen.

Lewis `Thompson showed the use of finely divided iron for this purposein 1839, and Victor Adler, in 1880, obtained patents in Germany claimingthe use of finely divided iron and other metals which have the propertyof combining with and transmitting carbon, for the same purpose.

John E. Bucher, in 1912, led and'later x obtained patents for .the useof finely divided iron in the fixation of nitrogen as sodium cyanide.

I have shown in a previous application for a process for formin nitrogencompounds, filed in the U. S. atent Oflice. August 19, 1916, Serial No.115,758, that alkalimetal cyanides may be formed in substantialvquantities by heating alkai-metal carbonate and carbon alone innitrogen without the use of catalyzers to temperatures commerciallyavailable which do not cause undue deterioration of the retorts,providing the alkalimetal compound is brought into the most intimatephysical contact with the carbon and the nitrogen. I have shown in saidapplication -a means of establishing and maintaining these conditionswhich produce the necc sszliry contacts between vthe reacting materia s.

In a second application, Serial Number 137,808, tiled in the U. S.Patent Ofiice December 19, 1916, I have shown a method of preparingalkali-metal compounds and caron for treatment with nitrogen whereby thedesired intim-ate contact of the reacting elements necessary to formalkali-metal cyanides, when alkali-metal compounds and carbon are heatedalone in nitrogen, is established and maintained.

In a further study of the fixation of nitrogen as alkali-metal cyanidesmade with the object ofl reducing the temperature neces sary to formcyanides, when alkali-metal compounds, carbon and nitrogen are heated,or of materially increasing the yie` d of cyanides, I have made thediscovery that the addition of alkali-metal halides to a finely groundmixture of sodium carbonate and coke, charcoal or like forms of carbon,caused the formation of sodium cyanide at temperatures below those atwhich cyanide is formed when carbon and alkali-metal .compounds otherthan the halides are heated alone in nitrogen.

The nature of the new process may bewhich I have carried out:

' Experiment #1.

illustrated by the following experiments A charge made up of finelydivided in- Experiment #2d The same mixture of sodium carbonate, cokeand sodium chloride, when heated in a retort for four hours at 800 to850 C. (pyrometer reading) with nitrogen under a pressure of 15 lbs. persq. in., showed on analysis 16.5% of sodium cyanide and no sodiumcyanamide.

Experiment #3.

The same mixture when heated in the retort for six hours under the sameconditions of temperature and nitrogen pressure showed on analysis 20.3%of sodium cyanide and no cyanamde.

I also made the discovery that the addition 'of alkali-metal halidestogether with the oxides of certain metals or with the metalsparticularly when they are present in a fine state of division to amixture of sodium carbonate, coke, charcoal, and the like, caused amaterial increase in the formation of sodium cyanide in a shorter time,when the mixture was heated in contact with free nitrogen, whether pureor mixed with other gases, than when the alkali-metal halides alone orthe metallic oxides or the metals alone were used. i

The process involving the conjoint use of alkali-metal halides withcertain metallic oxides or metals, in the formation of cyanide fromalkali-metal compounds, carbon and free or elemental nitrogen is fullydescribed in my companion application for Letters Patent Serial No.279802 tiled coincidently with this application in the United StatesPatent Ofiice. The present application is directed broadly to the use ofalkalimetal halides in the synthesis of alkali-metal cyanides.

ln view of the very striking results obtained in these experiments attemperatures at which there is little or no eyanideformation when sodiumcarbonate and carbon are heated alone in nitrogen, the experiments werecontinued on a semi-commercial scale, and the proportion of sodiumchloride was varied between Wide limits.

After many experiments with var ing proportions of sodium chloride, allof w ich gave cyanides at lower temperatures than they4 are usuallyformed, it was found that when the sodium chloride and the sodiumcarbonate were present in the charge in the proportion of the eutecticmixture (34.7 parts by weight of sodium chloride to 65.3 parts by weightof sodium carbonate) the highest yields of cyanide were obtained in agiven time.

The charges which gave the best average results were made up of from 50to 60% of the eutectic-mixture, to 40 to` 50% of coke, charcoal, or amixture' of coke and charcoal, or coke with a small proportion ofsawdust added to give porosity to the charge under the influenceof heatby driving out the volatile products of the sawdust. Good yields arestill obtained, however, even if recieve the proportions of the reagentsare changed considerably from those above mentioned. Thus with 40 partsof sodium carbonate and 40 parts of coke, there may be used from 10 to25 parts of sodium chloride, although it has been found desirable to useabout equa-l parts of sodium carbonate and coke, the ratio of the one tothe other may vary without seriously decreasing the yield of cyanide.For instance, from 35 to 50 parts of sodium carbonate may be used with40 parts of coke, and instead of Ll0A parts of coke from 35 to 50 partsmay be used.

The average results of thirty-two experiments in whlch the charges wereheated for six hours at temperatures between 850 and 900o C. (pyrometerreadings) showed that 50% of the sodium carbonate present in theoriginal charge had been -converted intOi sodium cyanide, with some highyields in which 55, 57, 59, 61 and 71% of the sodium carbonate hadpassed into cyanide.

Sodium fluoride, when substituted 'for the chloride, gave equally goodand, under certain conditions, better results.

The exact function of the sodium chloride or fluoride in promoting theformation of alkali-metal cyanides at lower temperatures than they areusually formed is not well understood. Analyses of the finished productsshows the same amount of sodium chloride and fluoride as was present inthe original charges. There is no visible evidence of transformation ordecomposition of the chloride or fluoride taking place during thereaction and no plausible chemical reaction can be written showing theparticipation of the halogen compound in bringing about the combinationof sodium, carbon and nitrogen or their compounds to form sodiumcyanide.

In the absence of any tangible evidence of chemical action, the View isheld that the function of the halide compound in the reaction is aphysical one, and has to do with the Whole complex melting point diagramof the system.

Besides acting as a iiux and dissolving away protecting coatings ofalready formed cyanides, liquefaction of the mass allows nitrogen todissolve and increases the velocity of its action. These combinedphysical functions of the halide compound also bring about a moreintimate physical contact between the reactive elements of the chargeand oier an explanation of the lower temperature required for thecyanide formation.

The following equation (1) expresses in toto the generally acceptedreaction. by which sodium'cyanide is formed from sodium carbonate,carbon and nitrogen:

The chemistry of the reaction is more complicated than is indicated bythe above maare equation. We know, for example, that in carrying out theabove reaction in the ordinary manner by heating sodium Carbonate andcarbon in nitrogen at from 950-1000 C., if the nitrogen supply isinsuflicient, or cut off entirely, metallic sodium and also sodiumcarbide are formed as well as sodium cyanide.

ln the presence o a flux such as sodium chloride or sodium fluoride, ormixtures of the same, it is quite possible that the above reaction takesplace through a succession of progressive steps and that the nitrogen isfirst combined in an intermediate compound formed at lower temperature,through which it passes tra-nsitorily into the cyanide.

The presence of sodium cyananiide found in the product of experiment #1,given above, favors this view. We know from Drechsels reaction (Jr. pr.Chem. 1880, 2, 21-77) that in the presence of carbon alkalimetalcyanamides take up carbon and pass into cyanides at temperatures below800 C. F or this reason it was only in experiment #1, carried out at 730C., that any trace of cyanamide was found in the product. llnexperiments 2 and 3, conducted at temperatures above 800, only sodiumcyanide was found in the product.

Cyanamides in general are known to form at lower temperatures than thecorresponding cyanide, and the formation of sodium cyanide at lowertemperature through the physical agency of sodium chloride or fluoridemay possibly be explained by chemical reactions taking place in a mannersimilar to the following:

Combining all of these into one equation, we have the empiricalequation:

(i) Na2co3+4c+x2=2naon+aoo given above.

rlhe sodium chloride and fluoride, by their fluxing action, allow theabove reactions to come to equilibrium more speedily since they effectcloser hysical contact of the reacting materials. hus, these reactionsproceed to the right until true equilibrium is more nea-rly attained. Insupport of this View of the mechanism of sodium cyanide formation, thefollowing facts, which are well established experimentally, may becited:

1. Sodium oxide is always found in the finished product.

2. Sodium is reduced from sodium oxide at lower temperatures than fromsodium carbonate-Gmelin-Kraut 2,' 1; 285.

3. Sodium carbide is formed when sodium is acted upon by carbon orcarbon monoxide.

'4. Calcium carbide breaks down into a sub-carbide CaC' when heated withcalcium luoride. The sub-carbide absorbs nitrogen readily and formscalcium cyanamide; see

Allmand, Applied Electro-Chemistry, l1:81; Arnold 1912; and Knox,Fixation of Atmospheric Nitrogen, 91, 92. By analogy, sodium carbide mayfollow the same course.

lt is of course possible that there-action .only proceeds as far as theformation of sodium carbide which, being an unsaturated compound, takesup nitrogen directly to form cyanide:

or it may follow the same course as calcium carbide shown by Allmand:

which, on further heating, with carbon, ac-

cording to Drechsel, passes into cyanide:4

rl'he nitrogen required for the production of cyanides by this process,as stated above, may be free or elemental nitrogen in a pure state, orit may be mixed with other gases, as, for example, with carbon monoxide,as in roducer gas.

n operating with producer gas as the source of nitrogen, certainprecautions are necessary: Carbon dioxide destroys cyanide rapidly evenat high temperatures and the producer gas used must contain the minimumquantity of C()2 in order to obtain practical results. The cyanidecharge cannot be allowed to cool 0H' in producer gas, since theequilibrium for the equation gives almost pure CO above 900 C. while at500 to 600 C. the product is almost all C02. By observing the properprecautions, the same results are obtained with producer gas as withfree nitrogen.

'llhe nitrogen may be passed into or through the charge under ordinaryatmospheric pressure but I prefer to use an absolute pressure of about30 lbs. er sq. in. as it insures a higher concentration of the nitrogenin the charge and more intimate contact. The function of the pressure ispurely physical.

Although, as indicated above, the conditions under which the new processcan be carried out may be widely varied, one preterred embodiment of myprocess is exemplified in the following description taken in connectionwith the accompanying drawing which shows a view in vertical sectionthrough the center of an apparatus which I have found to be suitable forcarrying out' a valve 4 for introducing the nitrogen,theY

pipe 3 ending in a distributor 5 near the bottom of the retort. Acharging hol'e in the head 2 for introducing the charge is closed with aplug 6 and an outlet 7 1s also provided in the head 2 for the escape ofthe gases given oil' in the reaction, together with the excess ofnitrogen or producer gas used in the operation. The pipe 7 ends in across carrying the valves 8, 9 and 10 as shown. The pipe having valve 8leads to a manometer (not shown). The valve 9 is for taking gas samplesduring the operation. The retort is also fitted witha pyrometer pocket11 and a therinocouple 12 for indicating the temperature of the chargeduring the o eration. The retort proper is set inside o au outside ironcasing 13, covered with a fireclay composition 14 to protect it fromoxidation by the gases of the combustion chamber 15. The combustionchamber 15, in which the retort 1 and casing 13 are placed, is similarto the ordinary steel-soaking it furnace in which steel ngots are heatebefore being rolled.

Tn carrying out the operation of manufacturing sodium cyanide the retortl is first closed tight and the charge, which, for example, consists ofof the eutectic mixture and 40% of coke, equivalent to approximately 39%of sodium carbonate, 21% of sodium chloride, and 40% of coke,isrintroduced through` the charging hole until the retort is' filledabout two-thirds full. The retort is then placed inside the rotectiveiron casing within the furnace, an the'connections made to the manometerand to the source of nitrogen' supply, as indicated in the retortthrough the valve 4. The valve 8 is now o ened to the manometer and theoutlet or b ceder valve 10 adjusted, so that the desired absolutepressure Aof about 2 atmospheres is obtained inside the retort. Tn viewof the high temperature it is not practicable vto exceed a pressure ofabout 20 pounds per sq. in. above atmospheric pressure (i. e., 35 poundsabsolute pressure). The beneficial e'ect of pressure is noticemaneraconnections b roken to the nitrogen supplyl and the retort' sealed byclosing the valves 8, 9, 10 and 4f. The retort is then lifted from thefurnace by a suitable hoistand another` retort already charged set intheV furnace and the operation repeated.

The hot retort is transferred to a cooling room and when it has cooledto room temperature, its contents are dumped by removing the flangedhead 2; the flanged head is then again fastened to the retort and thelatter recharged, for the second opera'tion,

through the opening made by removing the plug 6.

.The product from the retort containing sodium cyanide is placed inair-tight cans until it can be extracted for the production of highgrade sodium cyanide or hydrolyzed for the production of ammonia by themeans usually employed for these purposes. To the resulting residue ineither case is added the necessary make-up of sodium carbonate andcarbon and after drying and thoroughly mixing the remade charge is againfurnaced for the production of more cyanide. This operation may berepeated until such time as the impurities from the coke have built upto such an extent that they interfere with the proper operation of theprocess, when the soluble sodium salts, consistin of sodium carbonate,sodium hydrate rom the oxide present) and sodium chloride, or fluor-1de, as the case may be, are dissolved from the insoluble carbonresidue, evaporated, drled, and made up with a new lot of carbon. Bylselecting a form of carbon low 1n ash the furnacing operation may berepeated many times before an entire removal of carbon becomesnecessary.

It will be understood that l may depart widely from the charges andproportions o the mixtures given above; that I may vary the proportionof chlorides or uorides to the other alkali-metal compounds, and that inplaceof alkali-metal carbonate l may use other compounds of thealkalimetals, such as sulphates, hydroxides, and the like; or that I mause varying proportions of a mixture o various alkali-metal halides inthe mixtures with other alkalimetal compounds and make many changes inthe methods of manipulation or of the aplll() menare paratus withoutdeparting from the spirit and scope of the invention.

Having thus 'described my invention, what i claim is:

l. The process of making an alkali-metal cyanide, which comprisesheatin'g in contact with nitrogen a mixture containing an alkali-metalhalide, a compound of an alkali-metal other than a halide, and carbon toa temperature suicient to edect a reaction between the carbon, nitrogenand the second alkali-metal compound to form an alkalimetal cyanide.

2. The process of making sodium cyanide which comprises heating inconta/ct with nitrogen a mixture containing a sodium halide, sodiumcarbonate, and carbon, to a temperature sucient to eect a reactionbetween the carbon, nitrogen, and the sodium carbonate to form sodiumcyanide.

3. The process of making sodium cyanide, which comprises heating incontact with nitrogen a mixture containinoe sodium Huoride,sodium'carbonate, and car on, to a 'temperature sudicient to edect areaction between the nitrogen, carbon and the sodium carbonate` to formsodium c anide.

4. The process of maklng an alkali-metal cyanide, which comprisesheating in contact with 'a nitrogen-bearing gas a mixture containing analkali-metal halide, a compound of an 'alkali-metal other than a halide,and carbon, to a temperature suicient to etect a reaction between thecarbon, nitrogen and the second alkali-metal compound to form analkali-metal cyanide.

5. The process omaking sodium cyanide which comprises heating in contactwith a nitrogen-bearing gas a mixture containing a sodium halide, sodiumcarbonate, and carbonto a temperature sucient to effect a reactionbetween the carbon, nitrogen, and

th?1 sodium carbonate to form sodium cyan1 e.

6. The process of making sodium cyanide, which comprises heatinlg 1ncontact with a nitrogen-bearing gas a mixture containing sodium iuoride,sodium. carbonate, and carbon, to a temperature suiicient to edect areaction between the nitrogen, carbon, and the sodium carbonate to formsodium cyanide.

7. rThe process of making en alkali-metal cyanide, which comprisesmaking'a mixture of an alkali-metal halide, a compound of analkali-metal other than a halide, and carbon, heating the mixture in aclosed retort to a temperature of from 800 to 970 C., and subjectmg theheated mixture to the action of nitro en, substantially as described.

.8. he process of making sodium cyanide, which comprises making amixture of a sodium halide, sodium carbonate and carbon, heating themixture in a closed retort to a` temperature of from 800 to 970 C., andsubjecting the heated mixture to the action of nitrogen, substantiallyas described.

9. rihe process of making sodium cyanide, which consists in making amixture ofsodium fluoride, sodium carbonate and carbon, heating themixture in a closed retort to a temperature of from 800 to 970 C., andsubjecting the heated mixture to the action ot nitrogen, substantiallyas described.

10. The'process of making an alkali-metal cyanide, which comprisesmaking a mixture of an alkali-metal halide, a compound of an'alkali-metal other thana halide, and carbon, heating the mixture in aclosed retort to a. temperature of from 800 to 97 0 C., and subjectingthe heated mixture to the action of a nitrogen-bearing gas,substantially as de scribed.

11. rihe process of making sodium cyanide, which comprises making amixture of a sodium halide, sodium carbonate and carbon, heating themixture in a closed retort to a temperature of from 800 to 970 C., andsubjecting the heated mixture to the action of a nitrogen-bearing gas,substantially as described.

12. The process of' making sodium cyanide, `which consists in making amixture of sodium iiuoride, sodium carbonate and carbon, heating themixture in a closed retort to a temperature of from 800 to 970 C., andsubjecting the heated mixture to the action of a nitrogen-bearing gas,substantially as described.

13. The process. of making an alkali-metal cyanide, which comprisesheating in contact with nitrogen underan absolute pressure of about twoatmospheres a mixture containing an alkali-metal halide, a compound ofan alkali-metal other than a halide, and carbon, to a temperaturesuiicient to effect a reaction between the carbon, nitrogen and thesecond alkali-metal compound to form an alkali-metal cyanide.

14. The process of making sodium cyanide which comprises heating incontact with nitrogen under an absolute pressure of about twoatmospheres a mixture containing a sodium halide, sodium carbonate, andcarbon,

to a temperature suicient to effect a reaction between the carbon,nitrogen, and the sodi-y um carbonate to form sodium cyanide.

1.5. The process of making sodium cyanide,'which comprises heating incontact with nitrogen under an absolute pressure of about two atmosheres a mixture containing sodilum uori e, sodiumcarbonate, and carbon,

to a temperature suicient to edect a reaction between the nitrogen,carbon and the sodium carbonate to form sodium cyanide.

16. The rocess of making an alkali-metal cyanide which comprises passingnitrogen gas under 'an absolute pressure of from about 23 to 35 poundsper square inch in contact with a mixture containing an alkalimetalhalide, a compound of an alkalimetal other than a halide, and carbon,while maintaining said mixture at a temperature suiiicient to etect areaction between the carbon, nitrogen and second alkali-metal compoundto form an alkali-metal cyanide,

17. rlhe process of making sodium cyanide which comprises passingnitrogen gas under an absolute pressure of from about 23 to 35 poundsper square inch in contact with a mixture containing a sodium halide,sodium carbonate and carbon, while maintaining said mixture at atemperature sufficient to eect a reaction between the carbon, nitrogenand alkali-metal compound to form sodium cyanide.

18. The process of makingv sodium cyanide which comprises passingnitrogen gas under an absolute pressure of from 23 to 35 pounds persquare inch in contact with a mixture containing sodium fluoride, sodium carbonate and carbon, while maintaim ing said mixture at atemperature suiiicient to effect a reaction between the carbon, nitrogenand sodium carbonate to form sodium cyanide.

19. The process of making an alkali-metal cyanide, which comprisesheating in a retort in contactwith nitrogen a mixture containing analkali-metal halide, a compound of an alkali-metal other than a halideand carbon, to a temperature suilicient to eiect a reaction between thecarbon, nitrogen and the second alkali-metal compound to form analkali-metal cyanide, and maintaining the nitrogen at a pressure alittle below the minimum pressure capable of causing injuriousdistortion of the retort at the temperature at whichit is maintainedduring the reaction.

20. rThe process of makin an alkali-metal cyanide which comprisesheating in -contact with .n nitrogen a mixture containing from 10 to 25parts of an alkali-metal halide, from 35 to 50 parts of a compound of analkali-metal .other than a halide, and from 35 to 50 parts of carbon, toa temperature sufiicient to effect a reaction between the carbon,nitrogen and the second alkali-metal compound to form an alkali-meta1cyanide.

' l Lemma 21. The process of making sodium cyanide which comprisesheating in -contact with nitrogen a mixture containin from 10 to 25parts of a sodium halide, rom 35 to 5() parts of sodium carbonate, andfrom 35 to 5() parts of carbon to a temperature sufiicient to eHect areaction between the carbon, nitrogen and the sodium carbonate to formsodium cyanide.

22. The process of making sodium cyanide, which comprises heating incontact with nitrogen a mixture containing from 10 to 25 parts of sodiumfluoride, from 35 to 5() parts of sodium carbonate, and from 35 to partsof carbon, to a temperature sufficient to effect a reaction between thecarbon. nitrogen and the sodium carbonate to form sodium cyanide.

23. The process of making an alkali-metal cyanide which comprisesheating in contact with nitrogen a mixture containing about 20 parts oflari alkali-metal halide, about 40 parts of a compound of analkali-metal other than a halide, and about 40 parts of carbon, to atemperature sufficient to effect a reaction between the carbon, nitrogenand the second alkali-metal compound to form an alkali-metal cyanide.

24. The process of making sodium cyanide which comprises heating incontact with nitrogen a mixture containing about 20 parts of sodiumhalide, about 40 parts of sodium carbonate, and about 40 parts ofcarbon, to a temperature suilicient to effect a reaction between thecarbon, nitrogen and the sodium carbonate to form sodium cyanide.

25. The process of making sodium cyanide which comprises heating incontact with nitrogen a mixture containing about 20 parts of sodiumfluoride, about 40 parts of sodium carbonate, and about 40 parts ofcarbon to a temperature suiiicient to effect a reaction between thecarbon, nitrogen and the sodium carbonate to form sodium cyav nide.

